JPS609863B2 - Method for manufacturing exhaust gas treatment catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a catalyst for treating nitrogen oxide-containing gas, which contains a large amount of dust emitted from heavy oil-fired boilers, coal-fired boilers, combustion furnaces attached to various chemical equipment, etc. The present invention relates to a catalyst that can be applied to a process for detoxifying and removing nitrogen oxides (hereinafter abbreviated as N○×) in exhaust gas.

There are adsorption methods, oxidation absorption methods, solidification collection methods, and catalytic reduction methods as methods for removing N○× from exhaust gas, but the catalytic reduction method, which does not require post-treatment, is economically and technically advantageous. Development efforts are being made in various areas.

There are two possible methods for the catalytic reduction reaction depending on the selection of the reducing agent, but the selective catalytic reduction method is economically advantageous as it is not affected by the presence or absence of oxygen in the exhaust gas.

The present invention relates to a catalyst that can be applied to this reaction, and since it is particularly advantageous to use nitrogen as a reducing agent, the present invention will be further detailed below using this method. Conventionally, porous refractory materials such as alumina, titania, zirconia, silica, diatomite, and zeolite have been used singly or in combination as carriers for catalysts applied to selective catalytic reduction processes, but none of them have been granulated. This method has disadvantages in that it is expensive to use, and the production cost of the catalyst increases because it supports an activation-imparting component.

By the way, there is almost no dust in the exhaust gas from distilled oil or gas fuels (e.g. LNG, LPG), so
It is possible to granulate the above-mentioned carrier into any shape such as spherical or cylindrical, and bring the exhaust gas into contact with the catalyst layer perpendicularly.

On the other hand, in order to develop exhaust gas treatment technology that contains a large amount of ducts such as boiler exhaust gas fueled by heavy oil or coal, garbage incinerator exhaust gas, and coke oven exhaust gas, it is necessary to take measures to prevent dust from accumulating in the catalyst layer. For this purpose, the catalyst shape is cylindrical,
Methods of making it easier for dust to pass through, such as by creating a honeycomb shape, and scattering adhering dust by moving a granular catalyst are being considered. A method to prevent this is also promising, and the present inventors are also working hard to develop a catalyst that can be applied to this method.

The optimal catalyst shape for this method is a plate-like structure, and since it is currently difficult to form the aforementioned porous refractory material into a large plate, it can be manufactured at an extremely low cost, is lightweight, and has considerable strength. We have investigated the use of calcium silicate molded bodies as a material that can be easily molded into any shape. The calcium silicate molded body, which is the carrier of the present invention, is made by mixing silicic acid and lime with inorganic additives such as clay, asbestos, glass fiber, etc. as necessary, and suspending the mixture in water.
Shaping and drying an activated slurry of calcium silicate crystals obtained by heating at 200 to 300 q○ under a pressure of about 0 k9' or by temporarily discontinuing the heating process and proceeding with the hydrothermal synthesis reaction and crystallization. Manufactured in

However, in the calcium silicate molded body obtained in this way, calcium oxide exists in a free state without bonding with silicic acid, so the carrier of the catalytic activity imparting component is alumina,
Many of them are inferior in performance compared to those that support porous materials such as titania and zirconia.

Therefore, methods can be considered such as pre-treating the molded body with sulfuric acid, ammonium sulfate, etc. to convert calcium oxide that interferes with the catalytic action into calcium sulfate, or treating the molded body as a mere base material and applying catalyst components. The present invention belongs to the latter category, and uses a colloidal solution in which ultrafine particles of silicic anhydride having properties similar to the silicic acid contained in calcium silicate are dispersed in water as an adhesive, and furthermore, a catalyst is added on top of the colloidal solution. A patent application has already been filed in 1973 regarding the method of applying the ingredients.
Although the application was filed under No. 74 (52.2.1 Breast) of Road 2-1, the present invention relates to this improvement. Specially exposed Showa 52-168
No. 74 (Japanese Unexamined Patent Publication No. 53-102288) discloses a method for dissolving a vanadium-containing compound, which becomes a vanadium oxide by firing, in a titanium oxide slurry when supporting a vanadium oxide on a molded body. using acid.

However, although the catalyst produced in this way shows excellent denitrification performance, it has a strong effect of oxidizing S02 to S03 at high temperatures, so catalyst components other than vanadium, such as tungsten, molybdenum, tin, zinc, and cobalt, are added. need to be improved. Since these substances are not main components but components, they need to be uniformly dispersed in the catalyst, and simply adding them has no effect. However, among these catalyst components, the compounds that are the raw materials for tungsten and molybdenum, which are particularly important for suppressing the oxidation of S02, have extremely low solubility in water, and organic weak acids such as oxalic acid have no effect on the catalyst. Since it is almost insoluble in substances that do not affect the catalyst, we searched for a substance that dissolves these components and at the same time enhances the catalytic activity, leading to the present invention.

To obtain oxides of tungsten and molybdenum, tungstic acid, ammonium baratungstate, phosphotungstic acid, ammonium phosphotungstate, molybdic acid, ammonium molybdate, phosphomolybdic acid, ammonium phosphomolybdate, etc. are calcined above the decomposition temperature. However, in order to uniformly disperse titanium oxide in the slurry of titanium oxide, it is desirable to form a solution, and the present inventors have found that an amine compound is effective as a method for dissolving it.
The atamine compound is preferably a substance that does not have a poisoning effect when catalyzed, such as aliphatic amines such as methylamine, dimethylamine, monoethanolamine, or amino alcohol. Compounds containing vanadium are also easily dissolved by heating with this type of amine compound. To further improve the performance, an aqueous solution of tin chloride, zinc nitrate, cobalt nitrate, etc. may be added to the slurry material. The slurry thus prepared is alkaline due to the addition of an amine compound, and has the ripple effect of not only high activity but also improved adhesion to molded objects. The reason why amine compounds are particularly effective as solvents for the catalytically active components of the present invention is that they are viscous, so that the catalytically active components of dissolved tungsten, molybdenum, vanadium, etc. It is easy to uniformly disperse the slurry, and the adhesiveness of the slurry itself increases, which has the effect of improving the adhesion to the molded body.

Here, if a colloidal solution in which ultrafine particles of silicic anhydride are dispersed in water is added to the above-mentioned slurry, the catalytic performance will be slightly lowered, but this will not impede the improvement of adhesion.

The present catalyst can be obtained by adhering the slurry to the molded body in this way and then drying and firing it.

[Example 1] (Manufacture of molded body) Silica sand (Si0293.2%, AI203 3.5%, F
e2030.6%, other 2.7%) 5 parts of quicklime, 4 parts of quicklime, 10 parts of asbestos, and 10 parts of water were mixed, and this was mixed into an inner volume of 24 parts with a diameter of 25 walls and a depth of 50 walls. After placing in an autoclave with a container and sealing it, the internal pressure was increased to 8k9/kg, the temperature was raised to 170°C, and the mixture was stirred at a speed of 100 times/min for 5 hours, and then the stirring was stopped and the air was released. After cooling, the internal pressure was slowly returned to normal pressure over 6 minutes.

The reactant was taken out of the autoclave and an active slurry of calcium silicate crystals was formed by natural curing.
After drying at 0 for 1 hour, a calcium silicate molded body was obtained. (
Preparation of catalyst) After heating and dissolving titanium oxide powder, 90 parts of ammonium paratungstate and 23 parts of ammonium metavanadate in 12 parts of monoethanolamine, water was added to make an aqueous solution of 70 parts. Add to obtain a uniform slurry.

The previously obtained molded body was dissolved in a colloidal solution (pH 3-4) containing 20-21% silicic anhydride and 0.04% or less sodium oxide.
), then soaked in the slurry prepared earlier to adhere uniformly to the surface of the molded body, air-dried at 120°C for an hour, then fired at 550°C for 3 hours to obtain 91% titanium oxide, 91% titanium oxide, Catalyst 1 containing 7% tungsten and 2% vanadium oxide was obtained.

[Comparative example]

Ammonia water (28%) 10 parts, ammonium paratungstate 9 parts, ammonium metavanadate 23 parts
After heating and melting, 700 parts of water was added.

Next, 90 parts of titanium oxide powder was added and mixed to obtain a uniform slurry. The previously obtained molded body is mixed with silicic anhydride 20~
It was soaked in a colloidal solution (pH 3 to 4) containing 21% and 0.04% or less of sodium oxide, and then soaked in the slurry prepared earlier to uniformly adhere to the surface of the molded object, and then air-dried.
When the catalyst was dried for 1 hour at 2000 qo and then calcined for 3 hours at 550 qo, the adhesion of the catalyst to the molded body was weak and exposed parts of the base material were observed. [Example 2] Using the molded product of Example 1, "supporting was performed using titanium oxide, ammonium paratungstate, ammonium metavanadate, ammonium molybdate, tin chloride, zinc nitrate, and cobalt nitrate by the method of Example 1. Catalysts 2 to 8 shown in Table 1, which have various combinations of catalyst components with titanium, tungsten, vanadium, molybdenum, tin, zinc, and cobalt.
I got it.

Table 1 [Example 3] 22 samples were used to evaluate the performance of catalysts 1 to 8. The catalyst was crushed into small pieces on 3 to 4 sides so that it could be filled into a stainless steel reaction tube of 20 mm, and an activity test was conducted under the test conditions shown in Table 2, and the results shown in Table 3 were obtained.

Table 2 Table 3

Claims (1)

[Claims] 1 A molded body mainly composed of calcium silicate is catalyzed with titanium oxide, vanadium oxide, one type of oxide among tungsten or molybdenum, and optionally one type of oxide among tin, zinc, and cobalt. In order to support the active ingredient, the molded body is immersed in a colloidal solution in which silicic anhydride is dispersed in water, and then the metal oxide to be supported or its raw material compound is dissolved in an amine compound to form a slurry-like material. 1. A method for producing a catalyst for treating a nitrogen oxide-containing gas using ammonia as a reducing agent, the method comprising immersing the catalyst in a gas containing ammonia.